[Backport] Fixed issue - #19346 Import data 2.2.6 Value for 'product_type' attribute contains incorrect value

[saphaljha]

Original Pull Request

magento#19408

Description (*)

Fixed issue - magento#19346
Import data 2.2.6 Value for 'product_type' attribute contains incorrect value

Since 'product_attribute' is reserved attribute,so we can restrict this type of attribute to be created by user.

Fixed Issues (if relevant)

Fixed issue - magento#19346
Import data 2.2.6 Value for 'product_type' attribute contains incorrect value

Manual testing scenarios (*)

1. create an attribute with code product_type http://i.prntscr.com/AwUJuhizQKatBwNwRa1S7Q.png with type: dropdown scope: global sortable, comparable: no
2. add it to a family and create a product.
3. go to import profiles download sample file then reimport sample file

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with unit/integration tests (if applicable)
• All automated tests passed successfully (all builds on Travis CI are green)